Aim: To examine the effects on rat aging of caloric restriction (CR1) and undernutrition (CR2) on the body and on testicular weights, on two enzymatic antioxidants (superoxide dismutase and catalase), on lipid peroxidation and on the expression of testicular aromatase and estrogen receptors (ER). Methods: CR was initiated in 1-month-old rats and carried on until the age of 18 months. Results: In control and CR2 rats an age-related decrease of the aromatase and of ER (alpha and beta) gene expression was observed; in parallel a diminution of testicular weights, and of the total number and motility of epididymal spermatozo was recorded. In addition, aging in control and CR2 rats was accompanied by a significant decrease in testicular superoxide dismutase, catalase activities, and an increase in lipid peroxidation level (thiobarbituric acid reactive substance), associated with alterations of spermatogenesis. Conversely, caloric restriction-treatment exerted a protective effect and all the parameters were less affected by aging. Conclusion: These results indicate that during aging, a low caloric diet (not undernutrition) is beneficial for spermatogenesis and likely improves the protection of the cells via an increase of the cellular antioxidant defense system in which aromatase/ ER could play a role.